1. Field of the Invention
The present invention pertains to rotary unions for semiconductor wafer applications, such as chemical/mechanical polishing. In particular, the present invention pertains to such rotary unions which conduct a supply of xe2x80x9cultra purexe2x80x9d water which contacts the semiconductor wafer and must therefore be chemically compatible with the semiconductor wafer.
2. Description of the Related Art
Silicon wafers are typically employed for the mass production of commercially important integrated circuits. A plurality of integrated circuit devices are formed on a silicon wafer substrate, layer by layer, and chemical/mechanical polishing (CMP) must be performed on the wafer, between layering steps. Layering is typically carried out using photolithographic techniques which require an accurately flat surface.
Planarization of silicon wafers provides the high degree of flatness required for integrated circuit fabrication using photolithographic techniques. The active surface of the wafer substrate is placed in contact with a rotating polishing pad in the presence of various chemical agents which can include deionized water, etchants and polishing slurries. The polishing of commercially significant silicon wafers can include a more aggressive material removal process in which a slurry of polishing particles includes a chemically reactive agent. While it is desirable to polish a semiconductor wafer as quickly as possible in order to obtain the desired flatness or planarization, it is important that the over polishing be avoided. This requires a constant or near constant monitoring of the polishing process.
One type of polish monitoring employed today uses optical and other types of sensors embedded in a polish table. As mentioned, slurries and other types of chemical mixtures are employed in chemical/mechanical polishing and other types of wafer treatments. Typically, the polish table is flooded with slurry which also covers or otherwise interferes with the monitoring instrumentation. Accordingly, it is customary to wash the active face of the monitoring instrumentation which may comprise, for example, the free ends of optical wave guides embedded in the polish table. A flushing medium is employed to displace slurry or other wafer treatment chemicals from the active surface of the monitoring instrumentation.
In addition to flushing away material from the active face of the monitoring instrumentation, the flushing media must be compatible with the semiconductor wafer in all respects, especially in the sense of being chemically compatible with the wafer substrate and the integrated circuit structures built on the water substrate. Water is frequently chosen as the flushing medium since it is relatively inert in many respects. However, even xe2x80x9cpurexe2x80x9d water must be treated to attain very high levels of chemical inertness with regard to the semiconductor wafer and the term xe2x80x9cultra purexe2x80x9d has been applied to describe these special requirements. In order to maintain its ultra pure qualities, even brief incidental contact with metallic components must be avoided.
As mentioned, chemical/mechanical polishing is carried out using a polishing table and accordingly a rotating support shaft is customarily employed. In addition, devices used to contact the wafer with the polishing pad are also rotationally driven. These types of wafer-holding devices, usually termed wafer carriers, oftentimes are called upon to supply a fluid as part of the wafer treatment process. Thus, fluid communication must be maintained between the rotating wafer carrier and an external, non-rotating source.
Rotary unions, such as those described in U.S. Pat. No. 5,443,416 provides continuous fluid communication between a fluid source and a fluid chamber associated with the rotating wafer carrier. Although similar in some respects, a rotating polish table is much more massive than typical wafer carriers, and is subjected to much greater forces. If a rotary union is to be provided with fluid communication, a different type of arrangement from those employed in wafer carriers is needed. And, if a rotary union of a polish table is required to provide continuous fluid communication, different arrangements, other than those employed with wafer carriers, must be provided. Solutions to these and other problems attendant with polish table used in chemical/mechanical polishing are continually being sought.
It is an object of the present invention to provide a rotating union for a polish table used in chemical/mechanical polishing of semiconductor wafers.
Another object of the present invention is to provide a rotary union of the above type which provides a continuous fluid communication from a remote stationary fluid source to the polishing table and semiconductor wafers.
A further object of the present invention is to provide rotating union of the above-described type which maintains the desired condition of ultra pure fluids, such as ultra pure water, as it flows through the rotary union to eventually contact directly or indirectly, a semiconductor wafer being treated on the polishing table.
These and other objects according to principles of the present invention are provided in a rotary union for mounting to a rotating element which has an element bore wall defining an element bore of preselected size. The rotary union maintains semiconductor wafer treatment fluids in an ultra pure condition and comprises a union stator having a support face, a union rotor having a support face and an opposed mounting face adjacent the rotating element and at least one mount for movably mounting the union rotor toward and away from the rotating element. The union rotor defines a union bore of smaller size than said element bore, a spring bias between said union rotor mounting face and said rotating element, biasing said union rotor away from said rotating element, and a face seal between said union stator support face and said the union rotor support face, said face seal in the form of a flat washer and comprised of expanded TEFLON material. The union rotor also defines a passageway for the semiconductor wafer treatment fluids, said passageway extending from said union rotor support face to a portion of said union rotor mounting face radially interiorly of said element bore wall.
Other objects according to principles of the present invention are attained in a rotary union for mounting to a metallic rotating element which has an element bore wall defining an element bore of preselected size. The rotary union maintains semiconductor wafer treatment fluids in an ultra pure condition and comprises a union stator having a support face, a union rotor having a support face and an opposed stepped mounting face adjacent the rotating element, the union stator and the union rotor of nonmetallic composition which maintains semiconductor wafer fluids in an ultra pure condition, and a plurality of elongated fasteners movably mounting the union rotor toward and away from the rotating element. The union rotor defines a union bore of smaller size than said element bore, a spring bias between said union rotor mounting face and said rotating element, biasing said union rotor away from said rotating element, and a face seal between said union stator support face and said the union rotor support face, said face seal in the form of a flat washer and comprised of expanded TEFLON material. The union rotor defines a passageway for the semiconductor wafer treatment fluids, said passageway extending from said union rotor support face to a portion of said union rotor mounting face radially interiorly of said element bore wall.